Partial Purification of Human Lymphocyte Activating Factor

Abstract

Lymphocyte Activating Factor (LAF) is a T lymphocyte stimulant released by human monocytes cultured for 18-24 h in tissue culture medium containing 5% human serum and the non-specific immunostimulant lipopolysaccharide. The purification of LAF is essentially the separation of low MW LAF (.apprx. 13,000) from the human serum proteins required for production of the activity. Hollow fiber ultrafiltration effected a rapid separation of low MW LAF from serum proteins, but with a yield of only 20% of the original activity. Isoelectric focusing (IEF) efficiently separates LAF from all traces of human serum, resulting in a purified sample containing no measurable protein and revealing no bands on polyacrylamide gels. The IEF purified material is about 2% of the low MW activity present in the unfractionated culture medium and is highly active in the biological assay system.